Composite panels are typically formed of a raw material that is mixed with a binder. The mixture proceeds to a forming station that produces a mat of material, which is then subjected to heat and pressure in a hot pressing process to form the panel. Exemplary composite panels include oriented strand board (OSB), medium density fiberboard (MDF), wafer board, and particle board.
In a typical manufacturing process for a composite panel, a binder is added to the raw material by mechanical action in a large rotating drum, or blender. Other additives may also be introduced via the blender, either in liquid or powdered form, such as dry catalysts, fire retardants and wax. A typical OSB blender is approximately 12 foot by 30 foot, and rotates at approximately 4–26 rpms. In the manufacture of OSB, for example, a powdered or liquid resin is added to wood flakes that are on the order of 0.025″ thick in such a blender. The resin acts as a “spot weld” between the wood flakes during the hot pressing process.
These rotary blenders spray or atomize liquid resin, as well as other liquid additives, into the blender at a rate dependent on the flow of raw material. Application rates in the manufacture of OSB, for example, are typically 2–4% resin solids to wood solids. Powdered resins and additives are blown or mechanically conveyed to the blender. In the case of powdered resin, the resin often falls off during conveying to the forming station.
U.S. Pat. No. 5,914,153 to Swink et al. discloses a blender formed of a tumbling drum for blending resin and wood flakes. Wood flakes are introduced into the tumbling drum. A spinning cup atomizes resin and disperses it into the drum in order to coat tumbling wood flakes.
Adding liquid resin by atomization or spraying in a blender is limiting in that the resin coverage is often inefficient and all the flakes are unevenly coated. In the case where powdered resin is added at a blender, the resin often falls off during conveying to the forming station. Thus, additional resin is required to achieve the required properties for the panel. This adds costs to the manufacturing process, and can negatively impact the properties of the composite panel.
It is an object of the present invention to provide a method and apparatus to introduce powdered additives at a forming station for a composite panel that reduces or wholly overcomes some or all of the difficulties inherent in prior known devices. Particular objects and advantages of the invention will be apparent to those skilled in the art, that is, those who are knowledgeable or experienced in this field of technology, in view of the following disclosure of the invention and detailed description of preferred embodiments.